Gene flow is the transfer of alleles between populations, increasing or decreasing genetic diversity. It occurs within and between species, with bacteria being able to transfer genes between species. Migration and pollen transfer are examples of gene flow, with some enhancing biodiversity and others limiting natural variation. Gene flow can erase unique traits and ecologists take precautions to avoid introducing unwanted genetic material. The net effect depends on the genes and population, with gene flow being critical for survival in some cases.
Gene flow is the transfer of alleles, various forms of a gene that codes for specific traits, between distinct populations of individuals. This can increase genetic diversity in some cases and reduce it in others, depending on the circumstances. It occurs both within populations of the same species and in populations of different species, in some cases. Trans-species gene transfer is rarer and usually seen among bacteria, which have the ability to transfer genes between species with the use of special proteins called plasmids.
In a simple example of gene flow, wildflower populations on either side of a cultivated area would be separated by distance and might start to develop slightly different traits, such as purple versus blue flowers. Insects, animals or agricultural implements could carry pollen from one side to another, introducing new alleles into the population. Purple flowers may develop more blue specimens and vice versa.
Animal populations often experience gene flow as a result of migration. This can be seen markedly in human populations. In the United States, for example, people of mixed race with alleles of different origins highlight the role that migrants have played in that country’s history. Migration doesn’t have to be permanent to have a genetic impact, as long as the travelers have enough time to breed with the residents and leave a genetic legacy behind.
Some forms of gene flow enhance biodiversity. They introduce new traits to a population, which can increase hardiness and variety. In other cases, they may limit natural variation. A dominant trait could quickly wipe out a more fragile recessive, for example, especially in a small isolated population. Over time, slightly different populations may become more homogenous in nature, with no distinct traits of their own.
This can be a problem for plant and animal populations on remote islands and in other isolated areas. These may begin to speciate, dividing into populations with distinct and clear differences. If genetic material from another source is introduced, these differences may be erased and unique traits developed in that environment may be lost. Ecologists working in environments sensitive to this problem take precautions to avoid introducing unwanted genetic material into their field work.
The net effect of this phenomenon may depend on the genes involved and the population. Sometimes, new infusions of alleles through gene flow are critical to survival, as seen with the Ashkenazi Jewish population, where many people carry dangerous genetic traits due to a historically insular culture. Intermarriage with people from other regions can reduce the risk of a carrier marriage that could lead to a child with a genetic disorder.
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